The entire disclosure of Japanese Patent Application No. 2000-110797 filed on Apr. 12, 2000 including specification, claims, drawings and summary is incorporated herein by reference in its entirety.
1. Field of the Invention
The present invention relates to an exhaust emission purifier having an exhaust purifying catalyst which is disposed in an exhaust gas passage in order to remove toxic substances from exhaust gas, and which is preferably provided in an exhaust passage of an internal combustion engine or waste processing facility.
2. Description of the Related Art
An automobile on which an internal combustion engine is mounted emits exhaust gas derived from combustion within the internal combustion engine, and the exhaust gas contains toxic substances such as CO, HC, and NOx. Therefore, catalyst for removing such toxic substance is provided in the exhaust system. Incidentally, such catalyst is exposed to various atmospheres. However, catalyst can maintain its purifying performance under limited conditions only, and its purifying performance may be impaired greatly, depending on operating conditions of the engine. Examples of operating conditions of the engine which greatly impair the purifying performance of catalyst include low-temperature operation, such as low-temperature startup, and idling operation; and high-temperature operation of an NOx trap catalyst at 600xc2x0 C. or higher.
In order to solve the above-described drawback, a technique disclosed, for example, in Japanese Patent Application Laid-Open (kokai) No. 10-266831 has been proposed in order to effectively decompose and reduce toxic components contained in exhaust gas, irrespective of operating conditions of an engine. In the xe2x80x9cexhaust gas purifierxe2x80x9d disclosed in the patent publication, a three-way catalyst unit is disposed in an exhaust passage of an engine, and in the three-way catalyst unit there is provided an electric circuit for bringing toxic components contained in exhaust gas into a plasma state to thereby decompose the toxic components. When exhaust gas passes through the three-way catalyst unit, toxic components are brought into a plasma state by means of electrical power supplied from the electric circuit and are thus decomposed, and the remaining toxic components not having become plasma are removed by the three-way catalyst unit.
However, in the above-mentioned conventional exhaust gas purifier, by means of electrical power supplied from the electric circuit, toxic components contained in exhaust gas are brought into a plasma state and are decomposed directly. Therefore, the conventional exhaust gas purifier involves a problem in that a large amount of electrical power is consumed. In addition, there is a possibly that components once dissolved bond to toxic components again, so that a sufficient purifying performance cannot be obtained. Moreover, in the conventional apparatus, toxic components which have not become plasma through application of electrical power are removed by the three-way catalyst unit, as described above, and such toxic components cannot be removed reliably when the engine operates under conditions which lower the purifying performance of the catalyst.
The present invention was accomplished to solve the above-described problem, and an object of the present invention is to provide an exhaust emission purifier which has a stable exhaust purifying performance and which can conserve electrical power.
In order to achieve the above object, the present invention provides an exhaust emission purifier comprising: catalyst disposed in an exhaust gas passage in order to purify toxic substances contained in exhaust gas; reaction adjustment means for adjusting catalytic reaction through application of an electric or electromagnetic field to the vicinity of a surface of the catalyst; status detection means for detecting a factor which affects the exhaust gas purifying performance of the catalyst; and control means for controlling the electric or electromagnetic field applied by the reaction adjustment means, on the basis of the factor detected by the status detection means.
Accordingly, on the basis of the factor which affects the exhaust gas purifying performance, the control means controls the reaction adjustment means, such that the reaction adjustment means adjusts catalytic reaction through application of an electric or electromagnetic field to the vicinity of the surface of the catalyst. Therefore, stable performance for purifying exhaust gas by means of catalytic reaction can be secured, and electrical power can be conserved as compared with exhaust emission purifiers in which toxic components contained in exhaust gas are brought into a plasma state and are decomposed directly.
Preferably, the status detection means detects a factor correlated with temperature of the exhaust purifying catalyst; and when the catalytic temperature falls within a temperature range in which the performance of the catalyst decreases, the control means increases the strength of the electric or electromagnetic field to thereby promote the reaction of the exhaust purifying catalyst. Further, preferably, the control means restricts the strength of the electric or electromagnetic field applied by the reaction adjustment means so as not to exceed a discharge limit electric field.
Specifically, preferably, the status detection means detects, as the factor which affects the exhaust gas purifying performance, one selected from a parameter which affects catalyst temperature, a parameter which affects catalyst reaction performance, a parameter which affects deterioration of the purifying performance of the catalyst, and a parameter which affects the purifying performance of the catalyst for a specific exhaust gas component.
Preferably, the status detection means detects, as the parameter which affects catalyst temperature, one selected from exhaust gas temperature, engine coolant temperature, and catalyst temperature; and on the basis of the parameter which is detected by the status detection means and which affects catalyst temperature, the control means controls the electric or electromagnetic field applied by the reaction adjustment means.
Preferably, on the basis of the parameter which is detected by the status detection means and which affects catalyst temperature, the control means judges whether the catalytic temperature falls within a temperature range in which the performance of the catalyst deteriorates; and when the catalytic temperature falls within the temperature range in which the performance of the catalyst deteriorates, the control means increases the strength of the electric or electromagnetic field applied by the reaction adjustment means.
Preferably, the control means controls the strength of the electric or electromagnetic field applied by the reaction adjustment means so as not to exceed a discharge limit electric field.
Alternatively, the status detection means detects, as the parameter which affects catalyst reaction performance, one selected from engine speed, exhaust gas flow rate, and engine load; and on the basis of the parameter which is detected by the status detection means and which affects catalyst reaction performance, the control means controls the electric or electromagnetic field applied by the reaction adjustment means.
Preferably, on the basis of the parameter which is detected by the status detection means and which affects catalyst reaction performance, the control means judges whether the engine is in an operation range in which the performance of the catalyst deteriorates; and when the engine is in the operation range in which the performance of the catalyst deteriorates, the control means increases the strength of the electric or electromagnetic field applied by the reaction adjustment means.
Preferably, the control means controls the strength of the electric or electromagnetic field applied by the reaction adjustment means so as not to exceed a discharge limit electric field.
Alternatively, the status detection means detects, as the parameter which affects catalyst temperature, one selected from exhaust gas temperature, engine coolant temperature, and catalyst temperature, and detects, as the parameter which affects catalyst reaction performance, one selected from engine speed, exhaust gas flow rate, and engine load; and on the basis of the parameter which is detected by the status detection means and which affects catalyst temperature and the parameter which is detected by the status detection means and which affects catalyst reaction performance, the control means controls the electric or electromagnetic field applied by the reaction adjustment means.
Preferably, the control means judges, on the basis of the parameter which is ,detected by the status detection means and which affects catalyst reaction performance, whether the engine is in an operation range in which the performance of the catalyst deteriorates and judges, on the basis of the parameter which is detected by the status detection means and which affects catalyst temperature, whether the catalyst temperature falls within a temperature range in which the performance of the catalyst increases; and when the engine is in the operation range in which the performance of the catalyst deteriorates and the catalytic temperature falls within the temperature range in which the performance of the catalyst increases, the control means decreases the strength of the electric or electromagnetic field applied by the reaction adjustment means.
Alternatively, the status detection means detects, as the parameter which affects deterioration of the catalyst reaction performance, the degree of a specific catalyst poisoning among a plurality of catalytic poisonings; and on the basis of the degree of the specific catalyst poisoning detected by the status detection means, the control means controls the electric or electromagnetic field applied by the reaction adjustment means.
Preferably, the status detection means detects, as the parameter which affects: deterioration of the catalyst reaction performance, the degree of a specific catalyst poisoning selected from: CO poisoning, O2 poisoning, NOx poisoning, and SOx poisoning; and when the degree of the specific catalyst poisoning detected by the status detection means exceeds a reference value set for the specific catalyst poisoning, the control means controls the electric or electromagnetic field applied by the reaction adjustment means in order to remove the specific catalyst poisoning to thereby regenerate the catalyst.
Alternatively, the status detection means detects, as the parameter which affects the purifying performance of the catalyst for a specific exhaust gas component, one selected from concentration of the specific exhaust gas component, emission amount of the specific exhaust gas component, and exhaust gas air-fuel ratio; and on the basis of the parameter which is detected by the status detection means and which affects the purifying performance of the catalyst for a specific exhaust gas component, the control means controls the electric or electromagnetic field applied by the reaction adjustment means.
Preferably, when, on the basis of the concentration or emission amount of the specific exhaust gas component detected by the status detection means, the specific exhaust gas component is judged not to be purified sufficiently, the control means increases the strength of the electric or electromagnetic field applied by the reaction adjustment means.
Preferably, when, on the basis of the concentration or emission amount of each of a plurality of specific exhaust gas components detected by the status detection means, the plurality of specific exhaust gas components are judged not to be purified sufficiently, the control means changes the frequency of electromagnetic waves successively to a plurality of frequencies corresponding to the plurality of specific exhaust gas components.
Preferably, when, on the basis of the exhaust gas air-fuel ratio detected by the status detection means, emission amount of the specific exhaust gas component is expected to increase, the control means increases the strength of the electric or electromagnetic field applied by the reaction adjustment means.
Preferably, the status detection means detects operating conditions of an apparatus which discharges exhaust gas to the exhaust gas passage; and on the basis of the operating conditions detected by the status detection means, the control means controls the electric or electromagnetic field applied by the reaction adjustment means while predicting changes in the operating conditions, such that response delay is compensated for.